In general, a titanium-containing molecular sieve catalyst is used in the conversion of saturated hydrocarbon to alcohol or ketone or in the hydroxylation of an aromatic compound, and also has high activity in the epoxidation of olefin using hydrogen peroxide. However, it is known that the titanium-containing molecular sieve catalyst rapidly becomes inactivated due to poisoning. Thus, in order to apply the epoxidation process of an olefin compound through reaction with hydrogen peroxide in the presence of a titanium-containing molecular sieve catalyst to the commercial preparation of olefin oxide or epoxide, a catalyst regeneration technique, which enables the repeated use of the catalyst, is essentially required along with reaction and process techniques for the prevention of rapid inactivation. Accordingly, various techniques related to the catalyst regeneration method have been proposed.
Particularly, a method of regenerating a titanium-containing molecular sieve catalyst is largely based on a calcination process and a solvent washing process. The calcination process is a typical catalyst regeneration technique, which is disclosed in U.S. Pat. Nos. 5,753,576, 5,741,749, 6,169,050, 6,380,119, and 6,790,969. Upon use of the calcination process, deposited carbon material is burned at a high temperature or thermally cracked to remove it, thus regenerating the catalyst. However, the above process deforms the catalyst due to the reaction at a high temperature and is difficult to apply to a reactor, such as a multi-tubular reactor or a jacket reactor. Hence, thorough research into catalyst regeneration methods using a solvent washing process has been conducted in recent years.
U.S. Pat. No. 5,916,835 discloses a method of regenerating an inactivated catalyst through a washing process using various solvents. According to this patent, in the case where the solvent washing process is conducted using methanol at 50˜250° C. for 0.5˜12 hours, the best catalyst regeneration effect can result. However, the above method suffers because a calcination step using oxygen at 400˜900° C. is additionally required, and whether the activity of the regenerated catalyst is maintained for a long period of time is not confirmed.
In order to increase catalyst regeneration efficiency and decrease the regeneration period, U.S. Pat. No. 6,066,750 discloses a method of regenerating a catalyst comprising adding ammonium or an alkali metal cation to methanol to regenerate a catalyst at 150˜250° C. However, in the case where the metal ion remains in the reactor after the catalyst regeneration process, it functions as an impurity and the used solvent is difficult to recover.
U.S. Pat. No. 6,063,941 discloses a catalyst regeneration method, in which the catalyst may be efficiently regenerated through a washing process that uses methanol and then 2˜5 wt % aqueous hydrogen peroxide having a pH of 4˜7, adjusted with sodium hydroxide (NaOH), at 50˜100° C. However, the result of the regeneration of the catalyst is not specifically described.
U.S. Pat. No. 6,403,514 discloses a catalyst regeneration method using 30 wt % aqueous hydrogen peroxide added with a fluorinated inorganic compound. However, after the regeneration of the catalyst, a calcination step using air or oxygen at 400˜600° C. is essentially required to remove the ion. In addition, although at least 80% of initial catalytic activity is reportedly restored, whether the activity of the regenerated catalyst is maintained for a long period is not mentioned.
Further, the method of regenerating a catalyst using aqueous hydrogen peroxide as an oxidant is also disclosed in U.S. Pat. No. 5,620,935, in which the maintenance of the reaction temperature near the boiling point of hydrogen peroxide is noted to be important for the regeneration of the catalyst. However, as the result of the regeneration, only the restoration of the initial catalytic activity is mentioned, and whether the activity of the regenerated catalyst is maintained for a long period of time is not confirmed.
European Patent No. 1,489,074 discloses a catalyst regeneration method using a methanol washing process, which is characterized in that methanol used for catalyst regeneration is recovered after a lapse of time equal to 2˜30% of the total time required for the regeneration process. As such, the catalyst thus regenerated is active for a long period of time of 300 hours or more. However, the catalyst regeneration method using the solvent alone is effective only in cases of partial inactivation. In the cases of considerable inactivation or drastic decrease in the activity of the catalyst due to a problem with the reactor, even though the catalyst is regenerated, the activity thereof is difficult to restore to a predetermined level or higher.